Postmenopausal osteoporosis is a condition of excessive skeletal fragility which results in low impact fractures. The best studied measurable determinant of skeletal fragility is low bone mass. One of the easily correctable, non-genetic determinants of bone loss is calcium nutritional deficiency, particularly for older women for whom secondary hyperparathyroidism is considered to be universal. Calcium nutritional deficiency may be due to low dietary calcium as well as low 25(OH)D which promotes calcium absorption. Numerous reports demonstrating a bone sparing effect, and a few reports demonstrating an anti-fracture effect of increasing calcium intake among vitamin D replete women strongly support the hypotheses that increasing calcium intake among vitamin D intake benefits bone health in older women. Small scale intervention studies have shown that older women who consume calcium intakes up to 2400mg/d have a reversal of secondary hyperparathyroidism and experience no adverse effects due to the "high", in terms of the American diet, calcium intake. Despite these data, the behavior of many in the scientific community indicates doubt about the therapeutic value of calcium. The proposed study is designed to test whether calcium supplementation alone (1500mg/d) or calcium 1500mg/d) plus vitamin D (800IU/d) reduces the incidence of fractures, eliminates secondary hyperparathyroidism, and halts bone loss in a population-based sample of women 60+ years of age. An Achilles heel for intervention trials is the problem of subject compliance. This study will use an electronic monitoring system to track the number of time the treatment bottle is opened. This compliance measure will be used, not only to determine the amount of medication taken, but as a method to counsel the study subjects regarding protocol problems. This is a valid method to determine compliance, far superior to the traditional pill counts, and thus a substantial aid to measure the anti-fracture efficacy of calcium alone or calcium plus vitamin D interventions.